Influenza viruses bud from the apical surface of polarized epithelial cells. The mechanism by which the budding is restricted to the apical surface remains unknown. We have shown that influenza viral envelope glycoproteins either hemagglutinin (HA) or neuraminidase (NA) when expressed from cloned cDNAs are also transported to the apical surface in absence of other viral proteins. Our goal is to define the structural features ("signals") of HA and NA involved in transport, sorting and polarized expression. We wll continue studying the function of different domains of HA and NA and make specific alterations in the nucleotide sequence of the insert DNA to achieve the desired changes in the amino acid sequence of the polypeptides. These altered cDNA clones will be expressed and the fate of these altered proteins will be followed. Thus, we hope to determine the role of the specific domains (or amino acid sequences) of HA and NA in expression, sorting, and transport as well as in the biological functions of these two important glycoproteins. We plan to continue using eukaryotic expression vectors to express these proteins in animal cells. We are using site-specific mutations, deletions, as well as chimeric fusions between different genes to achieve these objectives. In addition, we are expressing influenza viral HA and NA in yeast (Saccharomyces cerevisiae), which may be of potential use in the development of an improved subunit vaccine.